Method and apparatus for adaptive nonlinear equalization in a polarization multiplexing optical communication system

Abstract

A method and apparatus for adaptive nonlinear equalization, comprising: a horizontal polarization component compensation unit configured to calculate a linear damage value of an input signal, a nonlinear damage value of a horizontal component of the input signal, and a crosstalk value caused by a vertical component to the horizontal component, and compensate the horizontal component according to the linear damage value, the nonlinear damage value and the crosstalk value; and, a vertical polarization component compensation unit configured to calculate a linear damage value of the input signal, a nonlinear damage value of a vertical component of the input signal, and a crosstalk value caused by a horizontal component to the vertical component, and compensate the vertical component according to the linear damage value, the nonlinear damage value and the crosstalk value. With the present invention, Intra-channel nonlinear damage of a polarization multiplexing optical communication system is effectively compensated.

The invention claimed is: 
     
       1. A nonlinear compensation apparatus used in an adaptive nonlinear equalizer, comprising:
 a horizontal polarization component compensation unit configured to calculate a linear damage value of an input signal according to the input signal, calculate a nonlinear damage value of a component of the input signal in a horizontal direction and a crosstalk value caused by the component of the input signal in a vertical direction to the component of the input signal in the horizontal direction according to the input signal, and compensate the component of the input signal in the horizontal direction according to the linear damage value, the nonlinear damage value and the crosstalk value calculated by the horizontal polarization component compensation unit; and 
 a vertical polarization component compensation unit configured to calculate the linear damage value of the input signal according to the input signal, calculate the nonlinear damage value of the component of the input signal in the vertical direction and a crosstalk value caused by the component of the input signal in the horizontal direction to the component of the input signal in the vertical direction according to the input signal, and compensate the component of the input signal in the vertical direction according to the linear damage value, the nonlinear damage value and the crosstalk value calculated by the vertical polarization component compensation unit. 
 
     
     
       2. The apparatus according to  claim 1 , wherein the horizontal polarization component compensation unit calculates the nonlinear damage value of the component of the input signal in the horizontal direction, and the crosstalk value caused by the component of the input signal in the vertical direction to the component of the input signal in the horizontal direction at several sampling timings for each sampling point, according to the input signal. 
     
     
       3. The apparatus according to  claim 2 , wherein the horizontal polarization component compensation unit comprises: a plurality of first delayers, a plurality of second delayers, a plurality of first multipliers, a plurality of second multipliers, a plurality of first adders and a first sum adder, wherein,
 the plurality of first delayers are configured to delay the component of the input signal in the horizontal direction, respectively, according to a sampling interval; 
 the plurality of second delayers are configured to delay the component of the input signal in the vertical direction, respectively, according to the sampling interval; 
 each of the first multipliers is configured to multiply the component of the input signal in the horizontal direction at sampling timing (n−l), the component in the horizontal direction at sampling timing (n−m) by the conjugate of the component in the horizontal direction at sampling timing (n−l−m) for corresponding sampling point, so as to obtain the nonlinear damage value of the component of the input signal in the horizontal direction at the corresponding sampling point; 
 each of the second multipliers is configured to multiply the component of the input signal in the horizontal direction at sampling timing (n−l), the component in the vertical direction at sampling timing (n−m) by the conjugate of the component in the horizontal direction at sampling timing (n−l−m) for corresponding sampling point, so as to obtain the crosstalk value caused by the component of the input signal in the vertical direction to the component in the horizontal direction at the corresponding sampling point; 
 the plurality of first adders are configured to add the nonlinear damage value of the component of the input signal in the horizontal direction at the corresponding sampling point with the crosstalk value caused by the component of the input signal in the vertical direction to the component in the horizontal direction at the corresponding sampling point, respectively; 
 the first sum adder is configured to add a product of the component of the input signal in the horizontal direction and its coefficient of corresponding linear item at each sampling point, a product of the component of the input signal in the vertical direction and its coefficient of corresponding linear item at each sampling point, and a product of a calculation result of each of the first adders and its coefficient of corresponding linear item at corresponding sampling point, so as to obtain an output of the component of the input signal in the horizontal direction. 
 
     
     
       4. The apparatus according to  claim 1 , wherein the vertical polarization component compensation unit calculates the nonlinear damage value of the component of the input signal in the vertical direction, and the crosstalk value caused by the component of the input signal in the horizontal direction to the component of the input signal in the vertical direction at several sampling timings for each sampling point, according to the input signal. 
     
     
       5. The apparatus according to  claim 4 , wherein the vertical polarization component compensation unit comprises: a plurality of third delayers, a plurality of fourth delayers, a plurality of third multipliers, a plurality of fourth multipliers, a plurality of second adders and a second sum adder, wherein,
 the plurality of third delayers are configured to delay the component of the input signal in the vertical direction, respectively, according to a sampling interval; 
 the plurality of fourth delayers are configured to delay the component of the input signal in the horizontal direction, respectively, according to the sampling interval; 
 each of the third multipliers is configured to multiply the component of the input signal in the vertical direction at sampling timing (n−l), the component in the vertical direction at sampling timing (n−m) by the conjugate of the component in the vertical direction at sampling timing (n−l−m) at corresponding sampling point, so as to obtain the nonlinear damage value of the component of the input signal in the vertical direction at the corresponding sampling point; 
 each of the fourth multipliers is configured to multiply the component of the input signal in the vertical direction at sampling timing (n−l), the component in the horizontal direction at sampling timing (n−m) by the conjugate of the component in the horizontal direction at sampling timing (n−l−m) at corresponding sampling point, so as to obtain the crosstalk value caused by the component of the input signal in the horizontal direction to the component in the vertical direction at the corresponding sampling point; 
 each of the second adders are configured to add the nonlinear damage value of the component of the input signal in the vertical direction at corresponding sampling point with the crosstalk value caused by the component of the input signal in the horizontal direction to the component in the vertical direction at corresponding sampling point, respectively; 
 the second sum adder is configured to add a product of the component of the input signal in the vertical direction and its coefficient of corresponding linear item at each sampling point, a product of the component of the input signal in the horizontal direction and its coefficient of corresponding linear item at each sampling point, and a product of a calculation result of each of the second adders and its coefficient of corresponding linear item at corresponding sampling point, so as to obtain an output of the component of the input signal in the vertical direction. 
 
     
     
       6. A receiver used for a polarization multiplexing optical communication system, comprising:
 a receiver front end; 
 a dispersion compensation apparatus connected to the receiver front end; 
 an adaptive nonlinear equalizer connected to the dispersion compensation apparatus; 
 a frequency offset compensation apparatus connected to the adaptive nonlinear equalizer; 
 a carrier phase recovery apparatus connected to the frequency offset compensation apparatus; 
 a data recovery apparatus connected to the carrier phase recovery apparatus; 
 wherein the adaptive nonlinear equalizer is implemented through the nonlinear compensation apparatus according to  claim 1 . 
 
     
     
       7. The receiver according to  claim 6 , further comprising:
 an adaptive linear equalization and polarization demultiplexing apparatus disposed between the dispersion compensation apparatus and the adaptive nonlinear equalizer. 
 
     
     
       8. The receiver according to  claim 6 , wherein the frequency offset compensation apparatus is further configured to feed a frequency offset compensation result back to the adaptive nonlinear equalizer; and the carrier phase recovery apparatus is further configured to feed a phase recovery result back to the adaptive nonlinear equalizer. 
     
     
       9. A polarization multiplexing optical communication system, comprising the receiver according to  claim 6 . 
     
     
       10. The receiver according to  claim 7 , wherein the frequency offset compensation apparatus is further configured to feed a frequency offset compensation result back to the adaptive nonlinear equalizer; and the carrier phase recovery apparatus is further configured to feed a phase recovery result back to the adaptive nonlinear equalizer. 
     
     
       11. A polarization multiplexing optical communication system, comprising the receiver according to  claim 7 . 
     
     
       12. An adaptive nonlinear compensation method, comprising:
 a horizontal polarization component compensation step of calculating a linear damage value of an input signal, a nonlinear damage value of a component of the input signal in a horizontal direction and a crosstalk value caused by the component of the input signal in a vertical direction to the component of the input signal in the horizontal direction according to the input signal, and compensating the component of the input signal in the horizontal direction according to the linear damage value, the nonlinear damage value and the crosstalk value calculated in the horizontal polarization component compensation step; and 
 a vertical polarization component compensation step of calculating the linear damage value of the input signal, the nonlinear damage value of the component of the input signal in the vertical direction and a crosstalk value caused by the component of the input signal in the horizontal direction to the component of the input signal in the vertical direction according to the input signal, and compensating the component of the input signal in the vertical direction according to the linear damage value, the nonlinear damage value and the crosstalk value calculated in the horizontal polarization component compensation step.